Compounds capable of absorbing and/or emitting light can be ideally suited for use in a wide variety of optical and electroluminescent devices, including, for example, photo-absorbing devices such as solar- and photo-sensitive devices, organic light emitting diodes (OLEDs), photo-emitting devices, or devices capable of both photo-absorption and emission and as markers for bio-applications. Much research has been devoted to the discovery and optimization of organic and organometallic materials for using in optical and electroluminescent devices. Generally, research in this area aims to accomplish a number of goals, including improvements in absorption and emission efficiency, improvements in the stability of devices, as well as improvements in processing ability.
Despite significant advances in research devoted to optical and electro-optical materials, for example, red and green phosphorescent organometallic materials are commercial, and they have been used as phosphors in organic light emitting diodes (OLEDs), lighting and advanced displays. Many currently available materials exhibit a number of disadvantages, including poor processing ability, inefficient emission or absorption, and less than ideal stability, among others.
Especially, good blue emitters are very scarce. One big challenge is the stability of the blue devices. And the choice of the host materials has a great effect on the stability and the efficiency of the devices. The lowest triplet excited state energy of the blue phosphors is very high compared with that of the red and green phosphors, which means that the lowest triplet excited state energy of host materials for the blue devices should be even higher. So one of the problems is that there are very limited host materials to be used for the blue devices.
Generally, a chemical structural change will affect the electronic structure of the compounds, which thereby affects the optical properties of the compounds, for example, emission and absorption spectra. Thus, the compounds of this present invention can be tailored or tuned to a specific application that desires a particular emission or absorption characteristic. The optical properties of the metal compounds in this disclosure can be tuned by varying the structure of the ligand surrounding the metal center. For example, the metal compounds having a ligand with electron donating substituents or electron withdrawing substituents can be generally exhibit different optical properties, including emission and absorption spectra.
Owing to the potential of phosphorescent multidentate cyclometallated complexes for harvesting both electrogenerated singlet and triplet excitions to achieve 100% internal quantum efficiency, these complexes are good candidate for the emitting materials of OLEDs. Usually, there are “emitting portion” and “ancillary portion” in ligand of multidentate platinum complexes. If stabilizing substitution(s), such as conjugated group(s), aryl or heteroaromatic substitution(s) and so on, were introduced into the emitting portion. The “Highest Occupied Molecular Orbital” (HOMO) and/or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level may be changed. So the energy gap between the HOMO and LUMO can be tuned. Thus the emission spectra of phosphorescent tetradentate platinum complexes can be modified to lesser or greater extents, such that the emission spectra can become narrower or broader, and/or such that the emission spectra can exhibit a blue shift or a red shift.
Thus, a need exists for new materials which exhibit improved performance in optical emitting and absorbing applications. Accordingly, such compounds, compositions, and devices comprising the same are disclosed herein.